Palladium deposition



United States Patent 3,274,022 PALLADIUM DEPOSITION Richard N. Rhoda,Westlield, N..I., assignor to The International Nickel Company, Inc.,New York, N.Y., a corporation of Delaware N0 Drawing. Filed Mar. 26,1963, Ser. No. 267,947 6 Claims. (Cl. 117130) The present inventionrelates to electroless deposition of metal and, more particularly, toelectroless deposition of palladium on metallic substrates.

It is well known that copper and copper-rich alloys have considerableutility in the communications field. In producing connectors, circuitcomponents and other devices useful in the electronic communications artfrom copper and copper-rich alloys, it is often desirable to plate orcoat such alloys with palladium in order to minimize corrosion and toprovide low noise-level and low resistance contacts. While electrolyticand non-electrolytic methods of depositing palladium are known, suchmethods are not particularly well adapted for use in the production ofmany electronic components. Thus, for the production of componentshaving deep cavities, for example, connectors, or the production ofcomponents having electrically isolated islands of metal, for example,printed cir cuits, electrolytic methods of palladium deposition are notpractical. Electroless methods of palladium deposition known heretoforehave not been successful in producing relatively thick, continuouscoatings of palladium directly on copper and copper-rich alloys. In atleast one prior known electroless bath for depositing palladium, copperacts as a poison to halt the catalytic and autocatalytic deposition ofthe palladium. I Although attempts were made to overcome the foregoingdifiiculties and other disadvantages, none, as far as I am aware, Wasentirely successful when carried into practice commercially on anindustrial scale.

It has now been discovered that by means of a novel autocatalyticprocess, relatively thick, continuous deposits of palladium can beproduced on copper and copper-rich alloy substrates.

It is an object of the present invention to provide a novelautocatalytic process for the electroless deposition of palladium.

Another object of the invention is to provide a novel autocatalyticprocess for the electroless deposition of palladium on copper-richmetallic substrates.

The invention also contemplates providing a novel process for producingmetallic electronic components having a copper-rich base and a surfaceof palladium metal.

It is a further object of the invention to provide a novel bath for theelectroless deposition of palladium.

Other objects and advantages will become apparent from the followingdescription.

Generally speaking, the present invention contemplates a process for theelectroless deposition of palladium which comprises establishing anaqueous bath containing about 100 to about 350 grams per liter (g.p.l.)of ammonia substantially as ammonium hydroxide, up to about 80 g.p.l. ofethylenediaminetetraacetic acid (E.D.T.A.), about 0.04 to about 0.50g.p.l. of unsymmetrical dimethylhydrazine (U.D.M.H.) and about 1 toabout 20 g.p.l. of divalent palladium added advantageously astetramminepalladium (II) chloride, immersing or dipping a body having acatalytic surface in said aqueous bath while maintaining the temperatureof said bath at about 68 C. to about 100 C. to effect catalytic andautocatalytic deposition of metallic palladium from said bath on saidsurface while maintaining the concentration of U.D.M.H. within theaforesaid range. The present invention also contemplates the palladiumbath which contains water, ammonia, divalent palladium and U.D.M.H. asessential ingredients.

3,274,022 Patented Sept. 20, 1966 In carrying the invention intopractice, it is advantageous to maintain the composition of the aqueousbath within the compositional limits set forth in the table and tomaintain the temperature of said bath at about C.

TABLE Advanta- Illustrative Ingredient geous Rlange, Value, g.p.l.

NI-Ia -170 13 5-10 10 5-24 7. 9 0. 05-0. 45 0. 086 Balance BalanceDissolved in the divalent state.

Objects to be plated in the bath of the present invention and accordingto the process of the present. invention must have a surface of acatalytic metal such as aluminum, chromium, cobalt, copper, gold, iron,molybdenum, nickel, palladium, platinum, ruthenium, silver, tin,tungsten, and alloys rich in cobalt, nickel and/or copper. Of course,such objects can be composed of such a catalytic metal. The bath andprocess of the present invention are particularly adapted to be employedin the plating of copper and alloys rich in copper, that is, alloyscontaining more than about 60% copper. Alloys rich in copper includebrass, cupro-nickel, German silver and bronze.

Objects made of materials such as glass, plastics and ceramics which donot catalyze the reduction of palladium can be coated with a preliminarydeposit of a catalytic substance such as nickel, silver, palladium,etc., and thus, by this means, it is possible in accordance with thepresent invention to chemically deposit smooth and adherent plates ofpalladium on substantially any object.

A bath for the chemical deposition of palladium in accordance with thepresent invention is advantageously made by dissolvingtetramminepalladium II) chloride in an aqueous solution of ammoniumhydroxide to which is added E.D.T.A. as the disodium salt. Palladouspalladium can also be added to the ammoniacal bath of the presentinvention (that is, an alkaline bath containing ammonium hydroxide orfree ammonia) as palladous chloride and palladous nitrate. The bath canbe employed statically or in a dynamic system such as in a rotatingbarrel. When objects are ready to be plated, that is, when they havebeen carefully cleaned in the manner normal to electroplatingtechniques, the deposition bath is brought to or maintained at operatingtemperature and the requisite amount of U.D.M.H. is added to the bath.The object or objects to be plated are then brought in contact with saidbath. As plating progresses, periodic additions of U.D.M.H. should bemade to the bath so that the concentration thereof is maintained withinthe required limits. In general, plating resulting from chemicaldeposition in the bath proceeds at a deposition rate of about 40 toabout 60 microinches per hour. At these plating rates it has been foundto be advantageous to add about 0.48 gram of U.D.M.H. per hour to thebath for each 1000 square centimeters (cm?) of area being plated.Addition rates as high as about 2 grams of U.D.M.H. per hour per 1000cm. have been employed. Conveniently, these additions can be made inaliquot portions at intervals of about hour or, of course, the additioncan be continuous.

The proportions of ingredients in the aqueous baths of the presentinvention are important in that if divalent palladium and U.D.M.H. arepresent in too large a concentration, the baths will tend to decomposespontaneously. On the other hand, if too little of these ingredients arepresent, the plating rate will be very slOW. Too little amine, e.g.,ammonia, also causes low plating rates. Amounts of ammonia in excess ofabout 280 g.p.l. are usually not advantageous in that at the operatingtemperabetter understanding of the'invention, the following illustrativeexamples are given:

Example I An aqueous solution containing g.p.l. of palladous palladium,280 g.p.l. of ammonium hydroxide and 8 g.p.l. of the disodium salt ofE.D.T.A. was placed in a rotatable plating barrel and maintained at atemperature of 75 C. Enough U.D.M.H. was added to provide aconcentration of about 0.086 g.p.l. thereof in the solution. A brassobject having a surface area of 500 cm. was thoroughly cleaned andplaced in the solution in the barrel. The barrel was then rotated and atfifteen minute intervals, about 0.06 gram of U.D.M.H. was added to thesolution. After one hour, the brass sample exhibited an adherentmetallic deposit of palladium about 43 microinches thick.

Example II A bronze object having a surface area of about 500 cm. wassuspended in :a. U.D.M.H. containing solution as em ployed in Example I.The solution was maintained at 85 C. and the concentration of U.D.M.H.was maintained. Over a period of time, an adherent deposit of palladiummetal was obtained on the bronze sample.

Example 111 After being suspended for one hour at 90 C. in an aqueoussolution containing the same amounts of U.D.M.H., ammonium hydroxide andthe disodium salt of E.D.T.A. as employed in Example I but containing 10g.p.l. of palladous palladium, a brass object having a surface area of500 cm. was found to have an adherent deposit of metallic palladiumabout 59 microinches thick.

Example IV To an aqueous solution containing 5 g.p.l. of palladouspalladium, about 280 g.p.l. of ammonium hydroxide and about 0.08 g.p.l.of U.D.M.H. in a rotatable barrel, was introduced a brass object havinga surface area of about 500 cm. The barrel was rotated for about onehour while the temperature of the solution was maintained at about 83 C.and while the concentration of U.D.M.H. was maintained by additionsevery fifteen minutes of about 0.06 gram of U.D.M.H. After one hour, theobject was found to have an adherent plate of metallic palladium about45 microinches thick.

Example V Boiling aqueous solutions containing 10 g.p.l. of palladouspalladium, 280 g.p.l. of ammonium hydroxide and 0.08 g.p.l. of U.D.M.H.were employed to plate copper and bronze objects. The objects each hadabout 500 cm. surface area. After one hour, during which the U.D.M.H.concentration was maintained by periodic additions, the copper objectsuspended in the bath exhibited a metallic palladium deposit about 60microinches thick, whereas the bronze object, plated in a rotatingbarrel, exhibited a metallic palladium deposit about 52 microinchesthick.

The foregoing examples contrast remarkably with the behavior ofspecimens made of copper or copper-rich alloys inserted inhydrazine-containing baths such as disclosed in US. Patent No.2,915,406. In the hydrazinecontaining baths no palladium is depositeddirectly on copper and/ or copper-rich alloys. In addition, under theprocess conditions of the present invention, hydrazine causescatastrophic deposition of palladium throughout the bath. Thus,hydrazine cannot be used as a substitute for U.D.M.H. in the process ofthe present invention.

The present invention is particularly applicable to the production ofelectrical and/or electronic components made of copper and coated withan adherent bright deposit of palladium. In employing the process andthe plating bath of the present invention, it is to be noted that otheringredients can be employed in the bath. For example, mole for moleamounts of stabilizing substances such as ammonium chloride and ammoniumsulfate can be employed in place of or in addition to E.D.T.A. Otheramines such as aminoethyl ethanolamine and/ or amylamine can be employedmole for mole in addition to or in place of part of the ammoniumhydroxide. In addition, substances for brightening, leveling, etc., canbe employed in the bath. Care must be taken, however, to excludesubstances such as iodide ion, stannous ion and other divalentpalladium, precipitants (for example, dimethylglyoxime, cyanides,thionalide, pyridine, hydroxyquinolines, metallic zinc and metallicmagnesium) from the bath.

It is to be noted that the present invention is not to be confused withprocesses for electroless deposition of palladium involving the use ofhydrazine. Objects made of copper or alloys rich in copper cannot bedirectly coated with palladium from ammoniacal baths containing highconcentrations of ammonia and containing hydrazine as the sole agent forreducing palladium ion to palladium metal. Thus, the process of thepresent invention is particularly adapted to be employed in the platingof electrical and electronic components made of copper and/orcopper-rich alloys.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

I claim:

1. A bath for the electroless deposition of palladium comprising anaqueous solution containing about 1 to about 20 grams per liter ofdivalent palladium, about 0.04 to about 0.50 gram per liter ofunsymmetrical dimethylhydrazine, an amine selected from the groupconsisting of ammonia, aminoethyl ethanolamine and amylamine in anamount equivalent in molar concentration to about 100 to about 350 gramsper liter of ammonia and a stabilizing agent selected from the groupconsisting of ammonium chloride, ammonium sulfate andethylenediaminetetraacetic acid in an amount equivalent in molarconcentration to up to about grams per liter ofethylenediaminetetraacetic acid.

2. A bath for the electroless deposition of palladium comprising anaqueous solution containing about 1 to 20 grams per liter of divalentpalladium, about 0.04 to about 0.50 gram per liter of unsymmetricaldimethylhydrazine, about to about 350 grams per liter of ammonia and upto about 80 grams per liter of ethylenediaminetetraacetic acid.

3. A bath for the electroless deposition of palladium comprisinganaqueous solution containing about 5 to about 10 grams per liter ofdivalent palladium, about 0.05 to about 0.45 gram per liter ofunsymmetrical dimethylhydrazine, about to about grams per liter ofammonia and about 5 to about 24 grams per liter ofethylenediaminetetraacetic acid.

4. A process for the electroless deposition of palladium which comprisesestablishing an aqueous bath containing about 1 to about 20 grams perliter of divalent palladium, about 0.04 to about 0.50 gram per liter ofunsymmetrical dimethylhydrazine, an amine selected from the groupconsisting of ammonia, aminoethyl ethanolamine and amylamine in anamount equivalent in molar concentration to about 100 to about 350 gramsper liter of ammonia and a stabilizing agent selected from the groupconsisting of ammonium chloride, ammonium sulfate andethylenediaminetetraacetic acid in an amount equivalent in molarconcentration to up to about 80 grams per liter ofethylenediaminetetraacetic acid and placing a body having a catalyticsurface in contact with said aqueous bath while maintaining thetemperature of said bath at about 68 C. to about 100 C. to effect adeposition of metallic palladium from said bath on said surface andwhile replenishing said bath with unsymmetrical dimethylhydnazine tomaintain the concentration thereof within said range of about 0.04 toabout 0.50 gram per liter.

5. A process for the electroless deposition of palladium which comprisesestablishing an aqueous bath containing about 100 to about 350 grams perliter of ammonia, up to amout 80 grams per liter ofethylenediaminete-traacetic acid, about 0.04 to about 0.50 gram perliter of unsymmetrical dimethylhydrazine and about 1 to about 20 gramsper liter of divalent palladium, placing a body having a catalyticsurface in contact with said aqueous bath while maintaining thetemperature of said bath at about 68 C. to about 100 C. to effect adeposition of metallic palladium from said bath on said surface andwhile replenishing said bath with unsymmetrical dimethylhydrazine tomaintain the concentration thereof within said range of about 0.04 toabout 0.50 gram per liter.

6. A process for the electroless deposition of palladium which comprisesestablishing an aqueous bath containing about 120 to about 170 grams perliter of ammonia, about 5 to about 24 grams per liter ofethylenediaminetetraacetic acid, about 0.05 to about 0.45 gram per literof unsymmetrical dimethylhydrazine and about 5 to about 10 grams perliter of divalent palladium, placing a body having a catalytic surfacein contact with said aqueous bath While maintaining the temperature ofsaid bath at about 68 C. to about 100 C. to effect a deposition ofmetallic palladium from said bath on said surface and while replenishingsaid bath with unsymmetrical dimethylhydrazine to maintain theconcentration thereof within said range of about 0.05 to about 0.45 gramper liter.

References Cited by the Examiner UNITED STATES PATENTS 2,915,406 12/1959Rhoda et al 117-430 X 3,156,634 11/1964 Duva et al 106-1 ALFRED L.LEAVITT, Primary Examiner. R. S. KENDALL, Assistant Examiner.

4. A PROCESS FOR THE ELECTROLESS DEPOSITION OF PALLADIUM WHICH COMPRISESESTABLISHING AN AQUEOUS BATH CONTAINING ABOUT 1 TO ABOUT 20 GRAMS PERLITER OF DIVALENT PALLADIUM, ABOUT 0.04 TO ABOUT 0.50 GRAM PER LITER OFUNSYMMETRICAL DIMETHYLHYDRAZINE, AN AMINE SELECTED FROM THE GROUPCONSISTING OF AMMONIA, AMINOETHYL ETHANOLAMINE AND AMYLAMINE IN ANAMOUNT EQUIVALENT IN MOLAR CONCENTRATION TO ABOUT 100 TO ABOUT 350 GRAMSPER LITER OF AMMONIA AND A STABILIZING AGENT SELECTED FROM THE GROUPCONSISTNG OF AMMONIUM CHLORIDE, AMMONIUM SULFATE ANDETHYLENEDIAMINETETRAACETIC ACID IN AN AMOUNT EQUIVALENT IN MOLARCONCENTRATION TO UP TO ABOUT 80 GRAMS PER LITER OFETHYLENEDIAMINETETRAACETIC ACID AND PLACING A BODY HAVING A CATALYTICSURFACE IN CONTACT WITH SAID AQUEOUS BATH WHILE MAINTAINING THETEMPERATURE OF SAID BATH AT ABOUT 68* C. TO ABOUT 100* C. TO EFFECT ADEPOSITION OF METALLIC PALLADIUM FROM SAID BATH ON SAID SURFACE ANDWHILE REPLENISHING SAID BATH WITH UNSYMMETRICAL DIMETHYLHYDRZINE TOMAINTAIN THE CONCENTRATION THEREOF WITHIN SAID RANGE OF ABOUT 0.04 TOABOUT 0.50 GRAM PER LITER.